This invention relates generally to an automatic transmission equipped with a torque converter comprising a pump, an impeller, a turbine runner and a stator and more particularly to a controller for a direct coupling clutch. It is known to provide a direct coupling clutch between the turbine shaft and the housing of the torque converter for directly coupling the input shaft of the torque converter and the turbine shaft as required. It is the conventional procedure to control engagement and disengagement of the direct coupling clutch by switching oil passages related to operation of the direct coupling clutch by actuating a switching valve of the spool-type. The valve operates in correspondence with pressure signals generated by the hydraulic control circuit of the automatic transmission. This requires complex control circuitry including the switching valve. If the spool valve became stuck for some reason, the direct coupling clutch cannot operate. Particularly, when the spool valve became stuck while the direct coupling clutch is engaged, the torque converter cannot function.
What is needed is a direct coupling clutch control system which operates automatically without use of special switch valves and circuitry, and protects the transmission and torque converter.